1. Field
This disclosure relates to an additive for a rechargeable lithium battery electrolyte, an electrolyte for a rechargeable lithium battery, and a rechargeable lithium battery including the same.
2. Description of the Related Technology
Relating to the recent tendency of down sizing and weight lightening of portable electronic devices, batteries used for a power source thereof are required to have a higher performance and a larger capacity. The commercially available rechargeable lithium battery has an average discharge potential of 3.7V, or around 4V, which is the essential item of the digital generation including a cellular phone, a laptop computer, a camcorder or the like, which are called 3C.
The rechargeable lithium battery is fabricated by using a material capable of reversibly intercalating/deintercalating lithium ion as a positive active material and a negative active material; injecting a liquid electrolyte or a polymer electrolyte between the positive electrode and the negative electrode. The rechargeable lithium battery includes a positive active material of lithium-transition metal oxide and a negative active material of lithium metal, lithium alloy, carbon (crystalline or amorphous) or carbon composite.
As the battery shows the characteristics by the complex reaction of a positive electrode/electrolyte, a negative electrode/electrolyte solution, and so on, using an appropriate electrolyte is one of important factors for improving the battery performance. When using a liquid electrolyte, an organic solvent having a low boiling point is used to enhance the low temperature performance. In this case, the organic solvent having a low boiling point is decomposed under the condition of allowed to stand at a high temperature, so as to occur a swelling phenomenon that the prismatic battery or pouch are swelled. Thereby, it may cause problems of deteriorating the battery reliability and safety at a high temperature.
In order to solve the problems, a vent or a current breaker may be provided to discharge the inner electrolyte solution when increasing the inner pressure at greater than or equal to the predetermined level, thus the rechargeable battery including the non-aqueous electrolyte solution may improve the safety. However, it may cause problems of miss-operation due to the inner pressure increase.
In addition, to suppress the inner pressure increase, it is known that the additives are injected to the electrolyte solution to change the SEI (Solid Electrolyte Interface) film forming reaction. For example, Japanese Patent Laid-Open Publication No. Hei. 9-73918 discloses a method of improving battery storability at a high temperature by adding less than or equal to 1% of diphenyl picrylhydrazyl compound; Japanese Patent Laid-Open Publication No. Hei. 8-321312 discloses a method of improving the cycle-life performance and the long-term storability by using 1%-20% of N-butyl amine compound in an electrolyte solution; Japanese Patent Laid-Open Publication No. Hei. 8-64238 discloses a method of improving the battery storability by adding 3×10−4 to 3×10−3 moles of calcium salt; Japanese Patent Laid-Open Publication No. Hei. 6-333596 discloses a method of improving the battery storability by adding an azo compound to suppress the reaction of between the electrolyte solution and the negative electrode. In addition, Japanese Patent Laid-Open Publication No. Hei. 7-176323 discloses a method of adding CO2 into the electrolyte solution; Japanese Patent Laid-Open Publication No. Hei. 7-320779 discloses a method of suppressing the decomposition of electrolyte solution by adding a sulfide-based compound into an electrolyte solution.
In order to improve the battery storability and stability, an appropriate film such as SEI film is provided on the negative electrode surface by adding a small amount of an organic material or an inorganic material. However, the added compound may be decomposed or may form an unstable film by interacting with the negative electrode of carbon at the initial charge and discharge according to the inherent electrochemical characteristics. Resultantly, the ion transportation is deteriorated in the battery, and gas is generated in the battery, and the inner pressure is increased even to deteriorate the storability, stability, cycle-life characteristics, and capacity of battery.